1. Technical Field
2. Background Art
Centrifuges generally work by spinning contained fluid samples at a sufficiently high rate of rotational speed to cause separation of the fluids into their component parts by centrifugal force. Research laboratories and hospitals often use electrically powered centrifuges that typically plug into a wall socket. These centrifuges are often very large and are not designed to be portable.
Known manually-powered centrifuges have a base that is clamped to a stationary device, such as a table. A handle is mounted to the base and spins samples supported on a rotary wheel above the base. The standard translation of motion is through the handle driving a worm gear, which drives a worm, which then drives the rotary wheel and samples. The base is generally narrower than the rotary wheel, and must be clamped to a stationary device, such as a table, in order to provide balance for the base and the spinning samples.
Standard manually-powered centrifuge designs have several drawbacks. Examples include Supertek, SYHD (a hand centrifuge by OEM), Whirlybird Centrifuge, etc. These centrifuges list max speeds at 3,000 rpm, but the sustained speed is closer to 1,000. This means that the forces generated are not high enough for all applications, for example, spinning blood to push red blood cells below a gel tube (such as BD VACUTAINER® SST™ and PST™ gel tubes) to ensure the sample does not remix during transport would not work with these centrifuges. Also, the time required to use these centrifuges is too much for comfortable use. They require about 10 minutes to separate blood fully, which technicians (based on field feedback) are unwilling to do. Applicants have heard from multiple locations in India that previously had this type of centrifuge, and technicians reported that they were unwilling to spin the device for this time. The technicians would just stop when they were tired, around 2-4 minutes of spinning, and decide it was good enough. Thus, blood samples are not fully separated, leading to inaccurate test results.
These types of centrifuges do not have an indication of completion. Rural non-technical people in the developing world, or even rural technicians, are not accustomed to using stopwatches and are unaware of the importance of maintaining a task for a specified amount of time. One cannot rely on a rural minimally trained person to be able to time something with a watch/stopwatch for the proper time.
These centrifuges also lack safety. The tube holders spin openly, where they could be dangerous to anyone who sticks their finger in that area. This is a real consideration in rural and village areas: as said by doctors who run a mobile clinic in India, “villagers tend to poke things.” There is also no containment if a tube holder breaks. These devices also have a c-clamp and therefore cannot be used without a table, which is unlikely to be available in a rural village setting.
The HANDYFUGE™ Plate Centrifuge (RPI) has a speed of 1,500 rpm/230 rcf obtained by pushing on a lever, and is specifically used for spinning down PCR plates. This device does have an enclosure and can be used on any flat surface, but is ineffective for similar reasons of speed as aforementioned standard manual centrifuges due to insufficient forces exerted on blood tubes. This device is also specifically tailored and marketed only for PCR plates and is not designed to fit standard blood tubes.
The Jabric manual centrifuge is able to reach high speeds of up to 5,000 G's with a complete enclosure of the samples. However, there is no indication that this is the “useable” speed, and in reality is likely lower as described above. The Jabric centrifuge is also nearly $1,000, making it unlikely to be affordable in rural areas and third world countries. If they could afford this price, a village could buy an electric generator and simply buy an electric centrifuge for around $50.
Multiple sources around the globe have come up with centrifuge designs out of readily available materials. These include a rural doctor in Nigeria at the Awojobi Clinic Eruwa who created both a bicycle-based and a hand-drill based centrifuge that reach 5,400 and 4,410 rpm, respectively. College students and professors have tried to solve the problem of a lack of an appropriate, affordable manual centrifuge by designing manual centrifuges out of salad spinners or egg beaters. Students at Rice University designed a salad-spinner-based centrifuge called the “sally centrifuge” that works for hematocrit only and only provides about 200 G force. An egg-beater based design reached 1,200 rpm or about 280 g-force (8 minutes of spinning required for complete plasma separation). These designs have not been successful due to issues with portability and commercial scalability.
Therefore, there remains a need for a centrifuge that is at a commercially affordable price (such as less than $200), has an indication of proper time and speed, does not require mounting to a table, is safe, and is able to operate with manual power at speeds required for complete blood separation in less than 4 minutes. There is also a need for a centrifuge with the ability to alternate between use of manual and electric power.